1. Field of the Invention
The present invention relates in general to a so-called hybrid drive system for driving a motor vehicle, and more particularly to improvements in such a hybrid drive system including a synthesizer mechanism for mechanically synthesizing outputs of an electric motor and an engine and transmitting a resultant of these outputs to a transmission.
2. Discussion of the Related Art
As a device for driving a vehicle such as an automobile, there has been proposed a hybrid drive system which is adapted to reduce exhaust gases and which includes (a) an electric motor operated by an electric energy, (b) an engine operated by combustion of a fuel, and (c) a synthesizer mechanism including hydraulically operated clutches and operatively connected to a transmission, for mechanically synthesizing an output of the electric motor and an output of the engine and transmitting a resultant of these outputs to the transmission. An example of such a hybrid drive system is disclosed in U.S. Pat. No. 5,258,651, wherein a planetary gear mechanism is employed as the synthesizer mechanism, and the electric motor is disposed radially outwardly of the synthesizer mechanism. In this hybrid drive system, the synthesizer mechanism, electric motor and engine are disposed coaxially with each other as an assembly within a single housing, and the transmission is connected to the output shaft of the synthesizer mechanism through a chain and is not disposed axially adjacent to the assembly.
Generally, the transmission indicated above incorporates hydraulically operated clutches and brakes for shifting actions, and requires lubrication of its components. Similarly, the synthesizer mechanism incorporates hydraulically operated clutches disposed between its components and between the components and the engine, and requires lubrication of its components. In the hybrid drive system wherein the transmission and the synthesizer mechanism are not disposed adjacent to each other, the hydraulic arrangement for the working fluid for the clutches and brakes and the lubrication arrangement tend to be undesirably complicated and suffer from difficult piping and formation of oil passages.